The present invention relates to an electrostatic latent image developing toner (hereinafter occasionally referred simply to as a toner), a developer, and an image forming method which are used in copier and printers.
In recent years, in almost all cases, high speed digital copiers, as well as laser printers, form images employing an electrostatic latent image developing system. In this field, in order to meet demands for achieving high image quality, toner comprised of particles having a small diameter, has received increasing attention. Further, in order to obtain the currently desired high quality images, polymerization toner has increasingly received attention as said electrostatic latent image developing toner.
Of polymerization toners, specifically, an emulsion aggregation type polymerization toner, which exhibits a narrow electrostatic charge amount distribution and makes it possible to obtain high resolution images, has received attention. Said emulsion aggregation type toner exhibits advantages in which it is possible to produce, without an increase in cost, toner comprised of particles having a small diameter which has a narrower size distribution than conventional particles. However, in order to introduce said toner onto the market, a way has been needed to enhance the control accuracy of the production process so that the toner particle diameter can be controlled as desired, while further decreasing the constituent toner particle diameter.
However, since said toner comprised of particles having a small diameter, when melted and deformed, exhibits less contact area as well as less adhesion force with recording materials or also called an image support which bears the final image, problems have occurred in which toner offsetting on the fixing member tends to occur. As a means to overcome said problems, when the molecular weight is adjusted so as to decrease the melt viscosity of said toner, problems have occurred in which the glass transition point of the resultant toner decreases, resulting in degradation of the storage stability of said toner.
Japanese Patent Publication Nos. 6-95228 and 7-101320 describe techniques which make said offsetting and said storage stability compatible with each other. In said techniques, toner resins are subjected to metal crosslinking. However, when applied to said toner comprised of particles having a small diameter, desired improvement of the resultant characteristics have not been achieved due to insufficient dispersion of inorganic salts.
On the other hand, Japanese Patent Publication Open to Public Inspection No. 11-311877 describes a technique which stabilizes toner charging characteristics as well as fixing characteristics such as a fixability temperature range. In said techniques, surface active agents as well as water-soluble inorganic salts are incorporated in said toner. However, it was found that said techniques did not result in charging characteristics or in fixing characteristics desired for said toner comprised of particles having a small diameter.
Further, since said toner comprised of particles, having a small diameter, has a relatively high electrostatic charge amount per unit weight, it is required to minimize variation of the electrostatic charge amount due to differences in humidity, as well as due to differences in printing modes such as a continuous mode or an intermittent mode. In order to meet said requirements, techniques have been employed in which charge control agents are used. However, the desired minimization has not been sufficiently achieved.
An objective of the present invention is to provide an electrostatic latent image developing toner, which exhibits excellent storage stability, minimizes variation of electrostatic charge amount due to high humidity, resulting in consistent production of high quality images while minimizing the variation of developed density, and a developer, as well as an image forming method using the same.
A production method of an electrostatic latent image developing toner is provided which is capable of controlling the toner particle diameter at high accuracy, and results in a narrow particle size distribution as well as a narrow electrostatic charge distribution. Further, an electrostatic latent image developing toner is provided in which variation of the electrostatic charge amount (an electric charge amount), due to differences in humidity as well as printing modes, is minimized.
The invention and preferred embodiments will now be described.
A toner for forming an electrophotographic image comprising a toner particle, wherein the toner particle comprises at least two inorganic salts having different valences. When xe2x80x9caxe2x80x9d (in percent) represents the ratio of the first inorganic salt contained in the greatest amount with respect to the total toner weight and xe2x80x9cbxe2x80x9d (in percent) represents the ratio of the second inorganic salt contained in the second greatest amount, the relationship described below is satisfied.
2.0xe2x89xa7axe2x89xa70.1
1.0xe2x89xa7bxe2x89xa70.01
7.5xe2x89xa7a/bxe2x89xa71.1
wherein the weight of xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d is the value in terms of anhydride.
A toner resin comprises polymerizable monomer having a carboxyl group in an amount of 1.0 to 12.0 percent, being the monomer weight ratio, as a recurring unit. The valence difference between the inorganic salt incorporated in toner in the greatest amount, and the inorganic salt incorporated in said toner in the second greatest amount is from 1 to 2.
Both the inorganic salt, incorporated in said toner in the greatest amount, and the inorganic salt, incorporated in the same toner in the second greatest amount, are chlorides.
The glass transition point of said toner is from 50 to 65xc2x0 C. during the first temperature increasing process and from 40 to 55xc2x0 C. during the second temperature increasing process.
Toner is prepared by aggregating resin particles and fusing those in a water based medium.
Toner comprises a crystalline organic compound and is prepared in such a manner that, after dissolving said crystalline organic compound, composite resinous particles prepared via the process which polymerizes said polymerizable monomers and colorant particles are salted out/fused.
Said toner is subsequently blended with a carrier and is then employed as a developer.
Said toner can be employed in an image forming method which converts an electrostatic latent image formed on a photoreceptor into a visible image, transfers said visible image onto a recording material, and thermally fixes the resultant image.
In such a process, an electrostatic latent image is preferably formed on the photoreceptor employing digital exposure.
In a production method of electrostatic latent image developing toner, in which toner particles are formed through salting-out/aggregating resinous particles in a dispersion comprising at least resinous particles, a production method of electrostatic latent image developing toner which comprises at least (1) a process for adding a salting-out agent which initiates growth of particles utilizing salting-out/aggregation (a salting-out/aggregating process), (2) a process for adding a salting-out termination agent when the particles reaches predetermined size (a particle growth terminating process), (3) a process for separating particles from said dispersion, and finally (4) a drying process.
The preferable volume average particle diameter of the particles (predetermined size) is 2-9 xcexcm.
Salting-out termination salts are salts having lower valence of those metal ions or positive ions than those of salting-out agents.
A dispersion comprises an anionic surface active agent, and the valence of metal ions or positive ions of a salting-out agent is to be divalent, and the valence of metal ions or positive ions of a salting-out termination agent is to be monovalent.
A dispersion comprises an anionic surface active agent, and the valence of metal ions or positive ions of a salting-out agent is to be trivalent and the valence of metal ions or positive ions of a salting-out termination agent is to be divalent or monovalent.
With regard to the volume average particle diameter after the drying process, when the particle diameter during the salting-out/aggregation process reaches 80 to 120 percent of the volume average diameter, a salting-out termination agent is added.